Because the handcuffs would come from exercising the War Power of the United States, and Congress has not acted to permit that.
There is much, much more to a state of war than the President and SECDEF moving troops around and having them kill people and break things.
This is an example of clear, unambiguous language which would permit (DID, in fact, permit) full press censorship:
"the President is hereby authorized and directed to employ the entire naval and military forces of the United States and the resources of the Government to carry on war against the Imperial Government of Japan; and, to bring the conflict to a successful termination, all of the resources of the country are hereby pledged by the Congress of the United States."
you need to be in a state of declared war to prosecute someone with a gov't security clearance from leaking information?